The controlling elements of maize are the best genetically characterized transposable elements in any higher organism due to the careful and perceptive studies that have been carried out by maize geneticists. Their work has shown that the maize elements differ from those described in prokaryotes in their mechanism of transposition and in their ability to modulate the activity of genes that come under their control. The extensive genetic information accumulated by maize geneticists can now be extended by work at the nucleic acid level. We have succeeded in cloning the wild-type Shrunken gene that encodes the enzyme sucrose synthetase and have descrived Ds controlling element insertions into the gene. We hope to elucidate the mechanism of transposition of maize controlling elements and to investigate their ability to regulate the activity of adjacent structural genes. These experiments involve molecular cloning, restriction analyses, and nucleic acid sequencing to determine the structure of portions of the controlling elements that might be involved in transposition. We also propose looking for transcripts encoded by controlling elements that are involved in controlling element functions and in the regulation of adjacent structural genes. The Shrunken locus is a convenient target for transpositions into and away from the gene. We have selected revertants of controlling element induced mutations and are seeking to identify insertions of other elements.